The present invention relates to an improvement in liquid-lubricated rolls of a type illustrated by U.S. Pat. No. 3,746,129, issued July 17, 1973 to George P. Knapp et al.
Curved rolls of a type conventionally used in processing paper, textiles, and other flexible sheet materials, comprise hollow annular roller means mounted by means of anti-friction bearings to rotate about elongated stationary axles, which are longitudinally curved to give the rolls the desired shape. The aforementioned U.S. Pat. No. 3,746,129 discloses and claims a roll which uses oil or other liquid to lubricate the bearings, in place of grease, to promote longer bearing life and to allow operation at higher speeds than are suitable for grease-lubricated rolls.
It is not acceptable to flood the bearings with liquid lubricant, since the submergence of their rollers or balls produces turbulent splashing that consumes an excessive amount of power to turn the roll, and generates an intolerable amount of heat. The aforementioned Patent provides means for maintaining a thin layer of lubricant on the inside of the roller during rotation, and for agitating the inner surface of this layer to generate a lubricating mist which passes into the bearings. Thus the bearings are lubricated without flooding, so long as the roll is rotating. However, a difficulty arises when the curved roll stops rotating for a time.
Except in the rare case where the plane of curvature of the axle is horizontal, the lubricant drains either to the midportion of the roll or to its ends, whichever happens to be lower. When rotation resumes, the lubricant will eventually distribute itself evenly throughout the length of the roll; however, this takes an appreciable time, during which the bearings in the vicinity of the lower parts of the roll remain flooded with lubricant. This increases the power consumed in turning the roll, which is wasteful and furthermore causes localized heating that adversely affects bearing life. Moreover, if the roll is oriented so that the lubricant collects at its ends, and if the end seal means are of the type which open when the roll turns faster than a specified speed, some of the lubricant may pass the seal means and be lost during the period of time when the lubricant is redistributing itself evenly through the length of the roll.
The general objects of this invention are to conserve power used in turning curved rolls, and to increase the life of their bearings. It is a specific object to provide a means for preventing lubricant from accumulating in the lowest longitudinal region of a curved roll when it is stationary, but for permitting the lubricant to distribute itself evenly through the length of the roll when the roll is rotating. Further objects and advantages of the invention will appear as the following description proceeds.
The invention is concerned with curved rolls of a kind known per se, having an elongated longitudinally-curved axle along which a series of anti-friction bearings are spaced by a series of interposed collars, and hollow annular roller means mounted on the bearings to form the rotating working surface for engaging whatever flexible sheet material is to be handled. The roller means may include a series of short cylindrical spools spaced end-to-end along the axle, each rotating on a different axis tangent to the curved axis of the axle at the location of that spool, and also includes a flexible annular surface sleeve, which is stretched over the full length of the roll and is supported by all of the spools in common. Alternatively, the spools may be omitted, and the roller means may comprise a self-supporting but flexible annular sleeve such as is described and claimed in U.S. Pat. Application Ser. No. 92,657, filed Nov. 25, 1970 and now U.S. Pat. No. 3,783,481 by James O. Gallant for "Curved Roll", and assigned to the assignee of this application.
As in the aforementioned U.S. Pat. No. 3,746,129, means are provided for maintaining a selected, limited volume of liquid in the annular passageway which is defined between the axle and the roller means and encloses the bearings. The volume is selected so that a thin layer of the liquid is formed on the inner circumferential surface of the roller means by centrifugal force as the roll turns at operational speeds, and the radial height of this rotating body of liquid extends to a level spaced radially outwardly from the axial openings between the races of the anti-friction bearings. Consequently, the rollers or balls of the bearings are not immersed in liquid, although open to the passageway.
Projections or studs are mounted on the axle and extend across the passageway slightly into the rotating body of liquid, to agitate the surface and produce a mist which fills the passageway and lubricates the bearings.
According to our improvement, we provide one or more barrier rings each of which is arranged adjacent to a corresponding bearing, and is specially constructed to pass lubricant lengthwise of the roll when it is rotating, but to block this flow when the roll is stationary. In a preferred form, the barrier rings are located in alternating sections of the annular passageway, which is subdivided by the bearings, and the aforementioned mist-forming studs are located in the remaining sections. Thus one axial face of each bearing is directly exposed to the lubricating mist, and yet the passageway is separated at fairly short intervals by the barrier rings.
When the roll stops, adjacent barrier rings prevent the quantity of lubricant contained in the passageway between them from escaping to accumulate in lower portions of the roll and flood the bearings situated there. If the barrier rings are spaced at suitably close intervals, re-starting therefore takes place with none of the bearings in an initially-flooded condition, and a corresponding savings in power consumption and bearing wear is realized.